Cellular telephone products can typically be powered using a 3.5 volt power supply, i.e. battery, and include a variable transmit power of 2.9 volts to 5.1 volts depending upon the status of the battery for example (i.e. low battery to battery recharge). Power controller circuits must have a power source with a minimum of -3.0 volts even as the system's power supply varies between 2.9 and 5.1 volts. However, as size and power requirements have developed, 4.6 volt battery sources have given way to 3.5 volt battery sources due to size and weight considerations. In order to further reduce size and weight of devices such as cellular phones, it is desirable to eliminate the use of inductive converters.
A device similar to that of the present invention is a three-diode voltage tripler. A three-diode voltage tripler is driven by dual 180.degree. out-of-phase outputs of an astable multivibrator. Such a device provides an output voltage of three times the multi vibrator's peak output minus 3 forward biased diode drops.
A typical problem encountered while attempting to use a three-diode voltage tripler is that its output impedance is more than an order of magnitude higher than what is required to properly source a power amplifier's power controller circuitry. The loading due to the power controller in effect reduces the available negative voltage to an unusable level.
Another device similar to that of the present invention can generally be classified as a charge pump. A charge pump essentially consists of two sets of double pole, double throw, switches with one set having closed contacts and the other set having open contacts. The sets alternate either open or close contacts at the frequency of the driving source which is typically an astable multivibrator.
A charge pump first operates in the charge mode by connecting a capacitor across the power source to be charged and then on the next half cycle disconnects this capacitor from the power source and enters pump mode by connecting the capacitor across a second capacitor and in the process adding a charge to the second capacitor. This ongoing process in time charges the second capacitor to a maximum possible voltage. The first capacitor is then inverted during the switching activity and actually charges the second capacitor to a negative voltage which becomes the supply needed to power the power controller circuitry.
A typical problem encountered when attempting to use a charge pump is that the negative voltage developed is only equivalent to about 65% of the positive supply voltage. This output of 65% would not be a problem if the low battery condition were 4.6 volts instead of 2.9 volts as is typical.
Please note that under the 2.9 volt "low-battery condition" this translates to a negative output of only -1.9 volts.